Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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014 FXUS63 KARX 151943 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 243 PM CDT Wed May 15 2024 .KEY MESSAGES... - Showers move through overnight with additional thunderstorms possibly developing east of the Mississippi River Thursday afternoon. Can`t rule out hail with storms tomorrow afternoon. - Seasonably warm temperatures in the 70s to low 80s through the weekend. - Next rounds of showers and storms come Saturday, more active period for showers and storms shaping up for the first part of next week (predictability low at the present time). && .DISCUSSION... Issued at 240 PM CDT Wed May 15 2024 Tonight and Thursday: Multiple Rounds of Showers and Storms A predominantly zonal flow exists this afternoon across the CONUS with a few waves of note across the country. One such wave axis was evident across the western Dakotas in water vapor imagery with a weak surface low reflection over the northern Siouxland region driving a broad swath of showers and isolated thunderstorms. This complex slides eastward tonight, with the short-range guidance struggling to resolve how the precipitation shield will evolve during this time owing to a lack of both instability and favorable wind profiles. Overall impacts tonight will be minimal outside of some heavier showers and occasional lightning. The convective complex works ahead of the surface front by the morning hours, and depending on how much recovery takes place in its wake, we may see redevelopment along the surface trough in the early afternoon on Thursday east of the Mississippi River. A 70-kt upper level jet overspreads the region as it rounds the base of the upper trough, lengthening hodographs ahead of the frontal boundary. The biggest question revolves around how much recovery can take place ahead of the front before it clears the region. The 12/18Z HRRR runs show about 1000-1400 J/kg of SBCAPE developing ahead of the trough, but it remains to see if this scenario will pan out. If storms do manage to form, hail of 1-2" in diameter would be the main threat. Explicit composite reflectivity progs from members of the 12Z HREF do lend credence to a line of convection developing by 18-20Z and exiting the area by 22-23Z, but a small change in the thermodynamic environment could quickly change this scenario. Linear hodographs would support storm splitters and mergers, so the line would grow upscale quickly as it advances eastward into south-central WI during the mid to late afternoon and morph into more of a wind threat. Saturday and Early Next Week: Next Rounds of Rainfall Split flow brings dry conditions for Friday, with the progressive flow ushering the next negatively-tilted shortwave through during the afternoon and evening on Saturday. With the shortwave already recoiling to the north and taking the 100-kt 300-mb jet with it, there is some uncertainty as to how much development takes place along the attendant surface front that slides into our area. Forecast soundings from the GEFS members don`t show much for inhibition ahead of this front (albeit with lower CAPE values), so it is probable that we`ll see some scattered storms with this surface forcing. Overall impacts will be limited in space and time owing to the lack of deep shear and compact hodographs. Attention then turns to early next week as longwave troughing deepens over the western CONUS, ejecting multiple weak perturbations through the region between Sunday and Tuesday. The subtle nature of these waves makes them tough to pin down more than a few days out. Looking though the 12Z guidance, odds are better that the surface baroclinic zone will stay south of the region and take the severe weather threat with it. That being said, there is plenty of variability in the ensemble members and such factors will be increasingly driven by how the previous day`s convection unfolds. This longwave ejects Tuesday and may be enough to lift the warm sector into the region, but confidence in such a scenario is low at the present time. Temperature Trends into Next Week Overall, expect at or slightly above average temperatures for the remainder of the week and into next week with highs in the 70s to low 80s and lows in the 40s and 50s. Despite the passage of a weak cold front Thursday night, warm 925-700-mb southwesterly flow builds in its wake across the High Plains for Friday and Saturday. Some of this warmer lower tropospheric air spills eastward into the Driftless region and allows highs to creep into the low 80s during this period. Confidence in the temperature forecast wanes slowly as we head through the first half of next week owing to the aforementioned precipitation uncertainties, but the pattern definitely favors at or above average temperatures with no cold snaps on the horizon. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1225 PM CDT Wed May 15 2024 VFR conditions are expected for the rest of the daytime hours, with ceilings gradually lowering overnight as rain showers move through from west to east. The heavier showers will be capable of MVFR/IFR visibility restrictions. A few thunderstorms are also possible, but confidence was not high enough to mention in the TAFs. These showers shift east of the Mississippi River for the morning hours. Ceilings fall to MVFR levels in the wake of these showers and persist for the remainder of the TAF period. Winds of 5-10 kts from the east/southeast this afternoon veer to the south overnight and continue shifting to the southwest Thursday morning. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Skow AVIATION...Skow